FOP: When Muscles Turn to Bone
August 18th, 2023 was one of the first days of school for the medical students at the University of Pennsylvania. They sat down for what seemed to be an average lecture, but soon turned out to be very different. Before them a man rolled up in his wheelchair, clearly lacking the mobility required for him to walk up on his own. This lecture wasn’t an information session with slides teaching students about the nuances of some diseases. This was a firsthand account of a patient with a rare disease called Fibrodysplasia ossificans progressiva (FOP). FOP is a rare disease in which a patient’s muscle regrows as bone, essentially locking the patient’s body up over time. There are only about 2,500 people affected with FOP in the entire world.
In a healthy human body, stem cells are stored to multiply and transform into any cell that may be lost or dying in the body. Stem cells change into the appropriate cell(muscle, bone, etc) because substances around the damaged cell bind to receptors of incoming stem cells, which communicate which type of cell is needed.
However, for those with FOP, this is not the case. In people affected with FOP, stem cells misinterpret the protein ACTIVIN-A as a signal to become bone. ACTIVIN-A expression can be caused in muscle after skeletal muscle injury. This causes damage in muscles, ligaments, and cartilage to regrow as bone, slowly locking up the patient’s body over time. FOP is a genetic disease, most often caused by a random mutation in a gamete of the parent.
There is still hope. In August of 2023, the FDA approved the first treatment for FOP called Sohonos (palovarotene).It reduces the occurrence of new abnormal bone formation in individuals with FOP by inhibiting a crucial process related to bone developement proteins (BMPs). There have also been methods for treatment for FOP for a little while. The FOP patient in the lecture spoke of nothing negative and talked about how, through the help of his doctors and modern medicine, having this disease allowed him to take on life to the fullest and live every moment as if it was his last. He spoke of the profound impact the healthcare professionals in his life had, and said without them he didn’t know where he would be, or even if he would be the same person. They kept him from being bedridden through constant care, allowing him to go out with friends and go to the gym for so many years of his life, before important muscles like his jaw, arms, and legs began to lock up.
https://www.ucsfbenioffchildrens.org/conditions/fibrodysplasia-ossificans-progressiva
